Lake Levels Plunge

A dry start to November 2007 has seen New Zealand’s hydro-electric lake levels plunge to levels lower than at the same time last year, in 2004 and in the dry year 1992 when blackouts were experienced.

Spring is normally a time of recovery for the nation’s hydro storage lakes, with warmer temperatures reducing demand and seasonal inflows from spring rain and snowmelt allowing the lakes to recover from the heavy demand of winter.

During October 2007, the seasonal trend appeared to apply, with good but erratic inflows bringing lake levels above 100% of average for the first time since February. However, the seasonal trend has not continued, and lake levels have plunged.

At the beginning of November, lake storage was at 2516 GWh (GigaWatt hours), 103% of average for the time of year. Storage then began falling at a steady rate, hitting 100% on the 4th, 90% on the 17th and 85% of average on the 19th.

Inflows over the same period hovered between 46% and 78% of average, while demand has generally been above last year’s figures.

Lake levels normally rise at this time of year, but in 2005 a steady decline sparked concerns of shortages during 2006 as lake levels approached those recorded during the 1992 crisis year. The latest plunge in storage has seen lake levels pass below 2006 levels when storage recovered dramatically during spring and, a few days later, below 2004 levels. About mid-November storage passed below post-winter 1992 levels.

Inflows normally decline from January, so increased supply from other energy sources and steady inflows will be necessary over the next 6 weeks to reverese the disturbing trend.

Trends indicate that the starting point for 2008 is looking better than the lead-in to both 1992 and 2006, if the decline is reversed during December.

[Compiled from data supplied by M-co.]

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